The present invention is directed to an improved surface treatment technique. In particular, the present invention is directed to a method of providing dynamic frictional surfaces, such as those disposed on new bearing components, with a surface finish that improves performance and extends service life.
In the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
Dynamic load-bearing devices, such as bearings, are well-known and widely utilized. Individual components within such devices have surfaces that in contact, an which move relative to one another. These surfaces (hereafter xe2x80x9cdynamic frictional surface(s)xe2x80x9d) are also provided with a particular surface finish during the manufacturing process, typically with the object of minimizing friction.
A continuous caster is a well-known device utilized in the steel manufacturing industry. Such devices produce cast steel products, such as elongated bars, strips, or sheets, that are moved over rollers. Bearings are utilized to support the dynamic rotary motion of the rollers. These rollers operate under very high-loads, due to the weight of the steel products moved over them, and a low speeds (i.e.xe2x80x94low rpm""s).
FIG. 1 is a cross sectional view of a bearing of the type which could be utilized in high-load, low-rpm applications such as mentioned above. FIG. 1 is illustrative of a typically constructed spherical roller bearing. This spherical roller bearing 1 as illustrated, includes an outer ring or race member 3. The outer ring 3 is annular in configuration and includes an outer diameter as well as an inner diameter defined by raceway surfaces 3a and 3b. The spherical roller bearing 1 further includes an annular inner race member 5 also comprising an inner diameter or bore, as well as an outer diameter defined by first and second race way surfaces 5a and 5b, as well as a central land surface 5c. A plurality of rolling elements 7 are disposed between the outer ring 3 and the inner ring 5. Each of the plurality of rolling elements 7 includes an outer rolling surface 7a. A cage member 9 acts to hold the rolling elements 7 in their proper position during operation.
Such bearing components are typically provided with what can be characterized as a relatively smooth surface finish. In this regard, typical surface roughness measurements for production bearings are on the order of:
These values can vary from manufacturer to manufacturer.
Surface roughness or texture can be measured in a number of ways. One typical way is to use an instrument that drags a stylus across a surface. As the stylus moves across the surface, the up and down movements are converted into a signal that is sent to a processor which produces an associated number value. One such number value is the xe2x80x9croot mean squarexe2x80x9d, or rms number. Another such number is the xe2x80x9cRAxe2x80x9d or arithmetic average roughness number. These values are typically reported in microinches (xcexcin) or micrometers (xcexcm). The meanings and derivation of these values are well-known to those of ordinary skill in the art.
However, bearings utilized in high lead, low rpm applications, such as continuous casters, have exhibited problems. The high-load, low speed conditions presented by the operation of the continuous caster negatively impacts the ability of the lubricant present within the bearing to operate effectively between the dynamic frictional surfaces. Consequently, the dynamic frictional surfaces can be damaged, as evidenced by the appearance of polishing, micro spalling, regular spalling, etc.
Thus, it would be advantageous to provide dynamic frictional surfaces of bearing components which operate under high-load, low speed conditions with properties and characteristics which improves their performance and extends service life.
The present invention solves the above-mentioned problems, and others, through the use of a technique for the treatment of dynamic frictional surfaces.
According to the present invention, it has surprisingly been found that if such dynamic frictional surfaces are provided with a surfaces finish which has a roughness that exceeds the typical new surface finish roughness, such surfaces exhibit unexpectedly superior benefits when utilized under high-load, low speed applications.
According to one aspect, the present invention provides a method of improving the performance and service life of a new bearing component, the component having at least one dynamic frictional surface the method comprising: subjecting the at least one dynamic frictional surface to a surface roughening operation thereby providing the surface with a surface roughness value RA of 18-80 xcexcin, preferably greater than 24 xcexcin, and most preferably 30-36 xcexcin.